SP5 Light and the Electromagnetic Spectrum Flashcards
What is a normal?
A line drawn at right angles to the barrier or mirror in a ray diagram
What is a ray diagram?
A way of modelling what happens when light is reflected or refracted
Where are the angle of incidence and the angle of refraction measured from?
The normal
State the law of reflection
When waves are reflected, the angle of reflection is equal to the angle of incidence
What happens to light when it travels through different materials?
It changes speed and direction
Define refraction
The change in the direction of a wave at a boundary
When is there no change in direction when a light ray hits the boundary?
If it hits the boundary at right angles
What is the medium light travels the fastest in?
Air
What is the medium light travels the slowest in?
Solids (glass)
What happens when light enters into a medium wherein it travels slower than the previous one?
It bends towards the normal
What happens when light enters into a medium wherein it travels faster than the previous one?
It bends away from the normal
What is total internal reflection?
Sometimes, when light is moving into a less dense material as compared to one it was already in, instead of being refracted, it is reflected inwards
When does total internal reflection occur?
The angle of incidence is greater than the critical angle and the incident material is denser than the second material
What are the two conditions for total internal reflection?
- angle of incidence > critical angle
- the incident material is denser than the second material
What is the critical angle?
The angle of incidence wherein the angle of refraction is 90 degrees
Why can luminous objects be seen?
They give off light
What is specular reflection?
Reflection from a smooth, flat surface
What is total internal reflection used in?
- prisms
- optical fibres
Describe a typical image produced from a specular reflection
- upright
- virtual
Define diffuse reflection
Instead of forming an image, the reflected light is scattered in all directions
What kind of image does a diffuse reflection cause?
- distorted
- no image at all
State the colours in order of increasing frequency and decreasing wavelength
- red
- orange
- yellow
- green
- blue
- indigo
- violet
When is light absorbed?
When white light shines on an opaque object
Give an example of the transmission of a wave at a boundary
Transparent objects, such as glass transmit waves because they barely absorb any light
What are filters?
Pieces of transparent materials that absorb some of the colours in white light and transmit a specific colour
When does an object appear black?
When it absorbs all wavelengths of visible light
What is a lens?
A shaped piece of transparent glass or plastic that refracts light
What does the power of a lens describe?
How much it bends light that passes through it
Describe a convex lens
- thicker in the middle than it is at the edges
- shaped like an almond/ eye
What is the focal point of a lens?
The point where all horizontal rays meet after passing through the lens
What is the focal length?
The distance between the lens and the focal point
What does a convex lens do?
Focuses light inwards
What is a convex lens used in?
- magnifying glasses
- to correct long-sightedness
- binoculars
Describe a concave lens
- ‘caves’ inwards
- thinner at the centre as compared to the edge
What does a concave lens do?
Spreads light outwards
What is a concave lens used for?
To correct short-sitedness
How is a concave lens drawn on a ray diagram?
With a straight line with arrows facing inwards
How is a convex lens drawn on a ray diagram?
A straight line with arrows on both sides
What is a real image?
An image produced on the opposite side of the lens to the object
What is a virtual image?
Appear to come from the same side of lens to object
What type of waves are electromagnetic waves?
Transverse waves
What are common properties amongst all electromagnetic waves?
- transfer energy as radiation from the source of waves to an absorber
- can travel through a vacuum
- travel everywhere at the same speed: 3x 10^8 m/s
What are EM waves with a slightly higher frequency than visible light called?
Ultraviolet
What are EM waves with a slightly lower frequency than visible light called?
Infrared
What is IR used for?
- electrical heating
- cooking food
- optical fibres
- security cameras
- thermal imaging cameras
What are the seven groups within the EM spectrum?
- radio waves
- microwaves
- IR
- visible light
- UV
- X rays
- Gamma rays
What are radio waves used for?
Communication: eg: broadcasting TV and radio communications and satellite transmissions. They can also induce oscillations in electrical circuits, as well as being produced by oscillations in electrical circuits
What waves can be refracted by the atmosphere?
Radio waves
What are the uses of microwaves?
- cooking food
- communications
- satellite comms
What waves are harmful to the human body?
Infrared, microwaves, ultraviolet, radio waves, x rays and gamma rays
How can a system stay at a constant temperature?
It must absorb the same amount of power as it radiates
What is power?
The amount of energy transferred in a certain time
What is Earth’s temperature dependant on?
- concentration of greenhouse gases
- rates of which light and IR radiation are:
—> absorbed by the Earth’s surface and atmosphere
—> emitted by the Earth’s surface and atmosphere
What happens when light and IR radiation are absorbed by the Earth’s surface?
- planet’s internal energy increases
- surface gets hotter
- some energy transferred to the atmosphere by conduction and convection
What happens when the Earth radiates lower frequency IR radiation?
- some absorbed by greenhouse gases
- greenhouse gases emit IR radiation in all directions; some out into space and some back towards earth
What is the ‘greenhouse effect’?
When the greenhouse gases in the Earth’s atmosphere trap heat, warming the Earth’s surface
What do greenhouse gases do?
Stabilise the surface temperature of the Earth, allowing the planet to sustain life
How is temperature affected if a system absorbs more power than it radiates?
It increases
What is causing an enhanced greenhouse effect?
Human activities such as deforestation and burning fossil fuels release more carbon dioxide into the atmosphere, which ends up retaining more heat
What is the relationship between wavelength and frequency of all EM waves?
Inversely proportional
- as wavelength increases, frequency decreases
- as frequency increases, wavelength decreases
How is temperature affected if a system radiates more power than it absorbs?
It decreases
How is the temperature of the Earth maintained?
By the amount of energy received and emmitted by the sun
What are the uses of UV?
- disinfectants
- security marking
- fluorescent lamps
- detecting forged bank notes
What are the uses of Gamma rays?
- sterilise foods and surgical instruments
- detection of cancer
- radiotherapy
What are the uses of xrays?
- observing the internal structure of objects
- airport security scanners
- medical x rays
What are the dangers of microwaves?
Internal heating of body cells
What is the danger of IR?
Skin burns
What is the danger of UV?
Damage to surface cells and eyes, which leads to skin cancer
What are the dangers of X rays and gamma rays?
Mutations or damage to body cells
